1. Field
This disclosure relates to a method and an apparatus for generating a phase coherent radio frequency (RF) signal.
2. Related Art
Waveform generators frequently include coherent frequency synthesis (CFS) to generate a train of finite-length phase-modulated RF signal segments (bursts) that differ in frequency, but which remain coherent in phase from burst to burst. That is, the generated waveform has the characteristic that the relative phase of any one segment (or burst) of the waveform is uniquely and predictably related to the relative phase of any other segment of the composite waveform. Such waveform generators are frequently implemented in applications such as, for example, RF communication, Doppler radar systems, Electromagnetic Warfare (EW) systems, navigation systems, and the like.
At the time of this writing, Holzworth Instrumentation, Inc., of Boulder Colo., USA, offered an RF synthesizer module, product no. HRB0220A, that offered broadband switching capabilities with fast frequency switching. The product included active phase memory.
Conventional CFS waveform generators have required the use of complex frequency multiplication and division techniques, mixing and filtering processes, and the generation of binary sequences at fairly high clock rates. Accordingly, an unfulfilled need exists for a CFS waveform generator that is low cost, easy to control, capable of high switching speeds, and can generate a large number (e.g., a million, a billion, or the like) distinct frequencies.